Ftm protocol with selectable acknowledgement format

ABSTRACT

Apparatuses and methods are disclosed that may perform ranging operations between a first device and a second device. The second device transmits an FTM request frame indicating a number of supported non-legacy ACK frame formats, and receives a first FTM frame indicating capabilities of the first device to receive each of the non-legacy ACK frame formats supported by the second device. The second device selects one of the non-legacy ACK frame formats or a legacy ACK frame format based, at least in part, on the indicated capabilities of the first device, and then transmits ACK frames using the selected frame format during the ranging operation.

TECHNICAL FIELD

The example embodiments relate generally to wireless networks, andspecifically to ranging operations performed between wireless devices.

BACKGROUND OF RELATED ART

The recent proliferation of Wi-Fi® access points in wireless local areanetworks (WLANs) has made it possible for positioning systems to usethese access points for position determination, especially in areaswhere there are a large concentration of active Wi-Fi access points(e.g., urban cores, shopping centers, office buildings, sporting venues,and so on). For example, a wireless device such as a cell phone ortablet computer may use the round trip time (RTT) of signals exchangedwith an access point (AP) to determine the distance between the wirelessdevice and the AP. Once the distances between the wireless device andthree APs having known locations are determined, the location of thewireless device may be determined using trilateration techniques.

Because ranging operations are becoming more important for positiondetermination, it is desirable to increase the accuracy of rangingoperations.

SUMMARY

This Summary is provided to introduce in a simplified form a selectionof concepts that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tolimit the scope of the claimed subject matter.

Apparatuses and methods are disclosed that may allow wireless devices toincrease the accuracy of ranging operations by transmitting both finetiming measurement (FTM) frames and acknowledgement (ACK) frames innon-legacy frame formats. The non-legacy frame formats may be associatedwith, for example, a high efficiency (HE) protocol, a very highthroughput (VHT) protocol, a high throughput (HT) protocol, and/or anyother high throughput protocol subsequently adopted by the Institute ofElectrical and Electronics Engineers.

In one aspect, a method is disclosed for initiating a ranging operationbetween a first device and a second device. The method may be performedby the second device by: transmitting, to the first device, a finetiming measurement (FTM) request frame indicating a number of non-legacyacknowledgement (ACK) frame formats supported by the second device;receiving, from the first device, a first FTM frame indicatingcapabilities of the first device to receive each of the number ofnon-legacy ACK frame formats supported by the second device; selectingone of the number of non-legacy ACK frame formats or a legacy ACK frameformat based, at least in part, on the indicated capabilities of thefirst device; and transmitting an ACK frame to the first device inresponse to reception of the first FTM frame, the ACK frame transmittedusing the selected ACK frame format.

In another aspect, a second device configured to initiate a rangingoperation with a first device is disclosed. The second device mayinclude one or more processors and a memory configured to storeinstructions. Execution of the instructions by the one or moreprocessors may cause the second device to: transmit, to the firstdevice, a fine timing measurement (FTM) request frame indicating anumber of non-legacy acknowledgement (ACK) frame formats supported bythe second device; receive, from the first device, a first FTM frameindicating capabilities of the first device to receive each of thenumber of non-legacy ACK frame formats supported by the second device;select one of the number of non-legacy ACK frame formats or a legacy ACKframe format based, at least in part, on the indicated capabilities ofthe first device; and transmit an ACK frame to the first device inresponse to reception of the first FTM frame, the ACK frame transmittedusing the selected ACK frame format.

In another aspect, a non-transitory computer-readable storage medium isdisclosed. The non-transitory computer-readable storage medium may storeone or more programs containing instructions that, when executed by oneor more processors of a second device, cause the second device toinitiate a ranging operation with a first device by performing a numberof operations. The number of operations may include transmitting, to thefirst device, a fine timing measurement (FTM) request frame indicating anumber of non-legacy acknowledgement (ACK) frame formats supported bythe second device; receiving, from the first device, a first FTM frameindicating capabilities of the first device to receive each of thenumber of non-legacy ACK frame formats supported by the second device;selecting one of the number of non-legacy ACK frame formats or a legacyACK frame format based, at least in part, on the indicated capabilitiesof the first device; and transmitting an ACK frame to the first devicein response to reception of the first FTM frame, the ACK frametransmitted using the selected ACK frame format.

In another aspect, a second device configured to initiate a rangingoperation with a first device is disclosed. The second device mayinclude means for transmitting, to the first device, a fine timingmeasurement (FTM) request frame indicating a number of non-legacyacknowledgement (ACK) frame formats supported by the second device;means for receiving, from the first device, a first FTM frame indicatingcapabilities of the first device to receive each of the number ofnon-legacy ACK frame formats supported by the second device; means forselecting one of the number of non-legacy ACK frame formats or a legacyACK frame format based, at least in part, on the indicated capabilitiesof the first device; and means for transmitting an ACK frame to thefirst device in response to reception of the first FTM frame, the ACKframe transmitted using the selected ACK frame format.

BRIEF DESCRIPTION OF THE DRAWINGS

The example embodiments are illustrated by way of example and are notintended to be limited by the figures of the accompanying drawings. Likenumbers reference like elements throughout the drawings andspecification.

FIG. 1 is a block diagram of a WLAN system within which the exampleembodiments may be implemented.

FIG. 2 is a block diagram of a wireless device in accordance withexample embodiments.

FIG. 3 is a signal diagram of an example ranging operation.

FIG. 4 is a signal diagram of another example ranging operation.

FIG. 5A is a signal diagram of a ranging operation in accordance withexample embodiments.

FIG. 5B is a sequence diagram depicting the ranging operation of FIG. 5Ain accordance with example embodiments.

FIG. 5C is a signal diagram of another ranging operation in accordancewith example embodiments.

FIG. 5D is a sequence diagram depicting the ranging operation of FIG. 5Cin accordance with example embodiments.

FIG. 6 depicts an example FTM Request frame in accordance with exampleembodiments.

FIG. 7 depicts an example ACK capabilities field in accordance withexample embodiments.

FIG. 8 depicts an example FTM frame in accordance with exampleembodiments.

FIG. 9 depicts an example ACK frame that may be used in accordance withthe example embodiments.

FIG. 10A depicts a legacy preamble of a frame that may be transmitted inaccordance with example embodiments.

FIG. 10B depicts a high throughput (HT) preamble of a frame that may betransmitted in accordance with example embodiments.

FIG. 100 depicts a very high throughput (VHT) preamble of a frame thatmay be transmitted in accordance with example embodiments.

FIG. 10D depicts a high efficiency (HE) preamble of a frame that may betransmitted in accordance with example embodiments.

FIG. 11 shows an illustrative flowchart depicting an example rangingoperation in accordance with example embodiments.

DETAILED DESCRIPTION

The example embodiments are described below in the context of rangingoperations performed by and between Wi-Fi enabled devices for simplicityonly. It is to be understood that the example embodiments are equallyapplicable for performing ranging operations using signals of othervarious wireless standards or protocols, and for performing rangingoperations between various devices (e.g., between a STA and a wirelessAP, between APs, between STAs, and so on). Thus, although the exampleembodiments are described below in the context of a WLAN system, theexample embodiments are equally applicable to other wireless networks(e.g., cellular networks, pico networks, femto networks, satellitenetworks), as well as for systems using signals of one or more wiredstandards or protocols (e.g., Ethernet and/or HomePlug/PLC standards).As used herein, the terms WLAN and Wi-Fi® may include communicationsgoverned by the IEEE 802.11 standards, Bluetooth, HiperLAN (a set ofwireless standards, comparable to the IEEE 802.11 standards, usedprimarily in Europe), and other technologies having relatively shortradio propagation range. Thus, the terms “WLAN” and “Wi-Fi” may be usedinterchangeably herein.

In addition, although described below in terms of an infrastructure WLANsystem including one or more APs and a number of STAs, the exampleembodiments are equally applicable to other WLAN systems including, forexample, multiple WLANs, Independent Basic Service Set (IBSS) systems,peer-to-peer systems (e.g., operating according to the Wi-Fi Directprotocols), and/or Hotspots. In addition, although described herein interms of exchanging data frames between wireless devices, the exampleembodiments may be applied to the exchange of any data unit, packet,frame, and/or signal between wireless devices. Thus, the term “frame”may include any signal, frame, packet, or data unit such as, forexample, protocol data units (PDUs), media access control (MAC) protocoldata units (MPDUs), and physical (PHY) layer convergence procedureprotocol data units (PPDUs). The term “A-MPDU” may refer to aggregatedMPDUs.

Further, as used herein, the term “HT” may refer to a high throughputframe format or protocol defined, for example, by the IEEE 802.11nstandards; the term “VHT” may refer to a very high throughput frameformat or protocol defined, for example, by the IEEE 802.11ac standards;the term “HE” may refer to a high efficiency frame format or protocoldefined, for example, by the IEEE 802.11ax standards; and the term“non-HT” may refer to a legacy frame format or protocol defined, forexample, by the IEEE 802.11a/g standards. Thus, the terms “legacy” and“non-HT” may be used interchangeably herein. Further, as used herein,the term “legacy ACK frame format” may refer to an ACK frame formatdefined by the IEEE 802.11a/g standards, and the term “non-legacy ACKframe format” may refer to an ACK frame format defined by the IEEE802.11n/ac/ax standards and/or to high throughput ACK frame formats thatmay be defined in one or more future IEEE 802.11 standards.

The terminology used herein is for the purpose of describing particularaspects only and is not intended to be limiting of the aspects. As usedherein, the singular forms “a,” “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” or “including,” when used herein, specify thepresence of stated features, integers, steps, operations, elements, orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components, orgroups thereof. Moreover, it is understood that the word “or” has thesame meaning as the Boolean operator “OR,” that is, it encompasses thepossibilities of “either” and “both” and is not limited to “exclusiveor” (“XOR”), unless expressly stated otherwise. It is also understoodthat the symbol “/” between two adjacent words has the same meaning as“or” unless expressly stated otherwise.

In the following description, numerous specific details are set forthsuch as examples of specific components, circuits, and processes toprovide a thorough understanding of this disclosure. Also, in thefollowing description and for purposes of explanation, specificnomenclature is set forth to provide a thorough understanding of theexample embodiments. However, it will be apparent to one skilled in theart that these specific details may not be required to practice theexample embodiments. In other instances, well-known circuits and devicesare shown in block diagram form to avoid obscuring the presentdisclosure. The term “coupled” as used herein means connected directlyto or connected through one or more intervening components or circuits.Any of the signals provided over various buses described herein may betime-multiplexed with other signals and provided over one or more commonbuses. Additionally, the interconnection between circuit elements orsoftware blocks may be shown as buses or as single signal lines. Each ofthe buses may alternatively be a single signal line, and each of thesingle signal lines may alternatively be buses, and a single line or busmight represent any one or more of a myriad of physical or logicalmechanisms for communication between components. The example embodimentsare not to be construed as limited to specific examples described hereinbut rather to include within their scopes all embodiments defined by theappended claims.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof, unless specificallydescribed as being implemented in a specific manner. Any featuresdescribed as modules or components may also be implemented together inan integrated logic device or separately as discrete but interoperablelogic devices. If implemented in software, the techniques may berealized at least in part by a non-transitory processor-readable storagemedium comprising instructions that, when executed, performs one or moreof the methods described above. The non-transitory processor-readabledata storage medium may form part of a computer program product, whichmay include packaging materials.

The non-transitory processor-readable storage medium may comprise randomaccess memory (RAM) such as synchronous dynamic random access memory(SDRAM), read only memory (ROM), non-volatile random access memory(NVRAM), electrically erasable programmable read-only memory (EEPROM),FLASH memory, other known storage media, and the like. The techniquesadditionally, or alternatively, may be realized at least in part by aprocessor-readable communication medium that carries or communicatescode in the form of instructions or data structures and that may beaccessed, read, and/or executed by a computer or other processor.

The various illustrative logical blocks, modules, circuits andinstructions described in connection with the embodiments disclosedherein may be executed by one or more processors, such as one or moredigital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), application specificinstruction set processors (ASIPs), field programmable gate arrays(FPGAs), or other equivalent integrated or discrete logic circuitry. Theterm “processor,” as used herein may refer to any of the foregoingstructure or any other structure suitable for implementation of thetechniques described herein. In addition, in some aspects, thefunctionality described herein may be provided within dedicated softwaremodules or hardware modules configured as described herein. Also, thetechniques could be fully implemented in one or more circuits or logicelements. A general purpose processor may be a microprocessor, but inthe alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices (e.g., a combinationof a DSP and a microprocessor), a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any othersuitable configuration.

FIG. 1 is a block diagram of a wireless system 100 within which theexample embodiments may be implemented. The wireless system 100 is shownto include four wireless stations STA1-STA4, a wireless access point(AP) 110, and a wireless local area network (WLAN) 120. The WLAN 120 maybe formed by a plurality of Wi-Fi access points (APs) that may operateaccording to the IEEE 802.11 family of standards (or according to othersuitable wireless protocols). Thus, although only one AP 110 is shown inFIG. 1 for simplicity, it is to be understood that WLAN 120 may beformed by any number of access points such as AP 110. The AP 110 isassigned a unique media access control (MAC) address that is programmedtherein by, for example, the manufacturer of the access point.Similarly, each of stations STA1-STA4 is also assigned a unique MACaddress. For some embodiments, the wireless system 100 may correspond toa multiple-input multiple-output (MIMO) wireless network, and maysupport single-user MIMO (SU-MIMO) and multi-user (MU-MIMO)communications. Further, although the WLAN 120 is depicted in FIG. 1 asan infrastructure BSS, for other example embodiments, WLAN 120 may be anIBSS, an ad-hoc network, or a peer-to-peer (P2P) network (e.g.,operating according to the Wi-Fi Direct protocols).

Each of stations STA1-STA4 may be any suitable Wi-Fi enabled wirelessdevice including, for example, a cell phone, personal digital assistant(PDA), tablet device, laptop computer, or the like. Each of stationsSTA1-STA4 may also be referred to as a user equipment (UE), a subscriberstation, a mobile unit, a subscriber unit, a wireless unit, a remoteunit, a mobile device, a wireless device, a wireless communicationsdevice, a remote device, a mobile subscriber station, an accessterminal, a mobile terminal, a wireless terminal, a remote terminal, ahandset, a user agent, a mobile client, a client, or some other suitableterminology. For at least some embodiments, each of stations STA1-STA4may include one or more transceivers, one or more processing resources(e.g., processors and/or ASICs), one or more memory resources, and apower source (e.g., a battery). The memory resources may include anon-transitory computer-readable medium (e.g., one or more nonvolatilememory elements, such as EPROM, EEPROM, Flash memory, a hard drive,etc.) that stores instructions for performing operations described belowwith respect to FIGS. 5A-5D, and 11.

The AP 110 may be any suitable device that allows one or more wirelessdevices to connect to a network (e.g., a local area network (LAN), widearea network (WAN), metropolitan area network (MAN), and/or theInternet) via AP 110 using Wi-Fi, Bluetooth, or any other suitablewireless communication standards. For at least one embodiment, AP 110may include one or more transceivers, one or more processing resources(e.g., processors and/or ASICs), one or more memory resources, and apower source. The memory resources may include a non-transitorycomputer-readable medium (e.g., one or more nonvolatile memory elements,such as EPROM, EEPROM, Flash memory, a hard drive, etc.) that storesinstructions for performing operations described below with respect toFIGS. 5A-5D, and 11.

For the stations STA1-STA4 and/or AP 110, the one or more transceiversmay include Wi-Fi transceivers, Bluetooth transceivers, cellulartransceivers, and/or other suitable radio frequency (RF) transceivers(not shown for simplicity) to transmit and receive wirelesscommunication signals. Each transceiver may communicate with otherwireless devices in distinct operating frequency bands and/or usingdistinct communication protocols. For example, the Wi-Fi transceiver maycommunicate within a 2.4 GHz frequency band, within a 5 GHz frequencyband in accordance with the IEEE 802.11 specification, and/or within a60 GHz frequency band. The cellular transceiver may communicate withinvarious RF frequency bands in accordance with a 4G Long Term Evolution(LTE) protocol described by the 3rd Generation Partnership Project(3GPP) (e.g., between approximately 700 MHz and approximately 3.9 GHz)and/or in accordance with other cellular protocols (e.g., a GlobalSystem for Mobile (GSM) communications protocol). In other embodiments,the transceivers included within each of the stations STA1-STA4 may beany technically feasible transceiver such as a ZigBee transceiverdescribed by a specification from the ZigBee specification, a WiGigtransceiver, and/or a HomePlug transceiver described a specificationfrom the HomePlug Alliance.

For at least some embodiments, each of the stations STA1-STA4 and AP 110may include radio frequency (RF) ranging circuitry (e.g., formed usingwell-known software modules, hardware components, and/or a suitablecombination thereof) that may be used to estimate the distance betweenitself and another Wi-Fi enabled device and to determine the location ofitself, relative to one or more other wireless devices, using rangingtechniques described herein. In addition, each of the stations STA1-STA4and/or AP 110 may include a local memory (not shown in FIG. 1 forsimplicity) to store a cache of Wi-Fi access point and/or station data.

For at least some embodiments, ranging operations described herein maybe performed without using the AP 110, for example, by having a numberof the stations operating in an ad-hoc or peer-to-peer mode, therebyallowing the stations to range one another even when outside thereception range of AP 110 or a visible WLAN (or other wireless network).In addition, for at least some example embodiments, ranging operationsdescribed herein may be performed between two APs that are in wirelessrange of each other.

FIG. 2 shows a wireless device 200 that may be one embodiment of thestations STA1-STA4 and/or AP 110 of FIG. 1. The wireless device 200 mayinclude a PHY device 210 including at least a number of transceivers 211and a baseband processor 212, may include a MAC 220 including at least anumber of contention engines 221 and frame formatting circuitry 222, mayinclude a processor 230, may include a memory 240, and may include anumber of antennas 250(1)-250(n). The transceivers 211 may be coupled toantennas 250(1)-250(n), either directly or through an antenna selectioncircuit (not shown for simplicity). The transceivers 211 may be used totransmit signals to and receive signals from AP 110, other stations,and/or other suitable wireless devices (see also FIG. 1), and may beused to scan the surrounding environment to detect and identify nearbyaccess points and other wireless devices (e.g., within wireless range ofwireless device 200). Although not shown in FIG. 2 for simplicity, thetransceivers 211 may include any number of transmit chains to processand transmit signals to other wireless devices via antennas250(1)-250(n), and may include any number of receive chains to processsignals received from antennas 250(1)-250(n). Thus, for exampleembodiments, the wireless device 200 may be configured for MIMOoperations. The MIMO operations may include SU-MIMO operations and/orMU-MIMO operations.

The baseband processor 212 may be used to process signals received fromprocessor 230 and/or memory 240 and to forward the processed signals totransceivers 211 for transmission via one or more of antennas250(1)-250(n), and may be used to process signals received from one ormore of antennas 250(1)-250(n) via transceivers 211 and to forward theprocessed signals to processor 230 and/or memory 240.

For purposes of discussion herein, MAC 220 is shown in FIG. 2 as beingcoupled between PHY device 210 and processor 230. For actualembodiments, PHY device 210, MAC 220, processor 230, and/or memory 240may be connected together using one or more buses (not shown forsimplicity).

The contention engines 221 may contend for access to one or more sharedwireless mediums, and may also store packets for transmission over theone or more shared wireless mediums. For other embodiments, thecontention engines 221 may be separate from MAC 220. For still otherembodiments, the contention engines 221 may be implemented as one ormore software modules (e.g., stored in memory 240 or stored in memoryprovided within MAC 220) containing instructions that, when executed byprocessor 230, perform the functions of contention engines 221.

The frame formatting circuitry 222 may be used to create and/or formatframes received from processor 230 and/or memory 240 (e.g., by addingMAC headers to PDUs provided by processor 230), and may be used tore-format frames received from PHY device 210 (e.g., by stripping MACheaders from frames received from PHY device 210).

Memory 240 may include a Wi-Fi database 241 that may store locationdata, configuration information, data rates, MAC addresses, and othersuitable information about (or pertaining to) a number of access points,stations, and/or other wireless devices. The Wi-Fi database 241 may alsostore profile information for a number of wireless devices. The profileinformation for a given wireless device may include informationincluding, for example, the wireless device's service set identification(SSID), channel information, received signal strength indicator (RSSI)values, goodput values, channel state information (CSI), and connectionhistory with wireless device 200.

Memory 240 may also include a non-transitory computer-readable medium(e.g., one or more nonvolatile memory elements, such as EPROM, EEPROM,Flash memory, a hard drive, and so on) that may store the followingsoftware (SW) modules:

-   -   a ranging SW module 242 to determine RTT values and/or to        estimate the distance between wireless device 200 and one or        more other devices, for example, as described below for one or        more operations of FIGS. 5A-5D, and 11;    -   a timestamp SW module 244 to capture timestamps of signals        received by wireless device 200 (e.g., TOA information) and/or        to capture timestamps of signals transmitted from wireless        device 200 (e.g., TOD information), for example, as described        below for one or more operations of FIGS. 5A-5D, and 11;    -   a protocol determination SW module 245 to determine the frame        format or protocol capabilities of one or more other wireless        devices, to announce the frame format or protocol capabilities        of wireless device 200 to one or more other wireless devices,        and/or to select a frame format or protocol for transmitting        frames (e.g., ACK frames, FTM frames, and/or other frames) to        one or more other wireless devices during ranging operations,        for example, as described below for one or more operations of        FIGS. 5A-5D, and 11;    -   a frame formation and exchange SW module 246 to create,        transmit, and/or receive frames to and from other wireless        devices, to embed frame format or protocol capability        information into frames transmitted to other wireless devices,        and/or to format ACK frames based, at least in part, on the        frame format or protocol capabilities of other wireless devices,        for example, as described below for one or more operations of        FIGS. 5A-5D, and 11; and    -   a positioning SW module 248 to determine the location of        wireless device 200 based, at least in part, on the distances        determined by the ranging SW module 242, for example, as        described below for one or more operations of FIGS. 5A-5D, and        11.        Each software module includes instructions that, when executed        by processor 230, cause the wireless device 200 to perform the        corresponding functions. The non-transitory computer-readable        medium of memory 240 thus includes instructions for performing        all or a portion of the operations of FIGS. 5A-5D, and 11.

Processor 230, which is coupled to MAC 220 and memory 240, may be one ormore suitable processors capable of executing scripts or instructions ofone or more software programs stored in wireless device 200 (e.g.,within memory 240). For example, processor 230 may execute the rangingSW module 242 to determine RTT values and/or to estimate the distancebetween wireless device 200 and one or more other devices. Processor 230may execute the timestamp SW module 244 to capture timestamps of signalsreceived by wireless device 200 (e.g., TOA information) and/or tocapture timestamps of signals transmitted from wireless device 200(e.g., TOD information). Processor 230 may execute the protocoldetermination SW module 245 to determine the frame format or protocolcapabilities of one or more other wireless devices, to announce theframe format or protocol capabilities of wireless device 200 to one ormore other wireless devices, and/or to select a frame format or protocolfor transmitting frames (e.g., ACK frames, FTM frames, and/or otherframes) to one or more other wireless devices during ranging operations.Processor 230 may execute the frame formation and exchange SW module 246to create, transmit, and/or receive frames to and from other wirelessdevices, to embed frame format or protocol capability information intoframes transmitted to other wireless devices, and/or to format ACKframes based, at least in part, on the frame format or protocolcapabilities of other wireless devices. Processor 230 may execute thepositioning SW module 248 to determine the location of wireless device200 based, at least in part, on the distances determined by the rangingSW module 242.

As mentioned above, the distance between a pair of devices may bedetermined using the RTT of signals exchanged between the devices. Forexample, FIG. 3 shows a signal diagram of an example ranging operation300 between a first device D1 and a second device D2. The distance (d)between the first device D1 and the second device D2 may be estimated asd=c*RTT/2, where c is the speed of light, and RTT is the summation ofthe actual signal propagation times of a request (REQ) frame and anacknowledgement (ACK) frame exchanged between device D1 and device D2.Device D1 and device D2 may each be, for example, an access point (e.g.,AP 110 of FIG. 1), a station (e.g., one of stations STA1-STA4 of FIG.1), or another suitable wireless device (e.g., wireless device 200 ofFIG. 2).

More specifically, device D2 may estimate the RTT between itself anddevice D1 using the time of departure (TOD) of the REQ frame transmittedfrom device D2, the time of arrival (TOA) of the ACK frame received bydevice D2, and the Short Interframe Spacing (SIFS) duration of deviceD1. The SIFS duration indicates the duration of time between device D1receiving the REQ frame and transmitting the ACK frame. The SIFSduration, a range of values for which are provided by the IEEE 802.11standards, provides Wi-Fi enabled devices time to switch theirtransceivers from a receive mode (e.g., to receive the REQ frame) to atransmit mode (e.g., to transmit the ACK frame).

Because different make-and-models (and sometimes even samemake-and-models) of communication devices have different processingdelays, the precise value of SIFS may vary between devices (and evenbetween successive frame receptions/transmissions in the same device).As a result, the value of SIFS is typically estimated, which often leadsto errors in estimating the distance between two devices. Morespecifically, the IEEE 802.11 standards define the SIFS duration as 10us+/−900 ns at 2.4 GHz, 16 us+/−900 ns at 5 GHz, and 3 us+/−900 ns at 60GHz. These “standard” SIFS durations include tolerances that maydecrease the accuracy of RTT estimates. For example, even if the SIFSduration of device D1 may be estimated within +/−25 ns, a ranging errorof +/−7.5 meters may result (which may be unacceptable for manypositioning systems).

To reduce ranging errors resulting from uncertainties in the value ofSIFS, recent revisions to the IEEE 802.11 standards call for eachranging device to capture timestamps of incoming and outgoing frames sothat the value of RTT may be determined without using SIFS. For example,FIG. 4 shows a signal diagram of an example ranging operation 400between device D1 and device D2 performed using Fine Timing Measurement(FTM) frames in accordance with the IEEE 802.11 REVmc standards. DeviceD1 and device D2 may each be, for example, an access point (e.g., AP 110of FIG. 1), a station (e.g., one of stations STA1-STA4 of FIG. 1), orother suitable wireless device (e.g., wireless device 200 of FIG. 2).For the example of FIG. 4, device D2 requests the ranging operation;thus, device D2 is the initiator device (or alternatively the requestordevice) and device D1 is the responder device. Note that the term“initiator device” may also refer to an initiator STA, and the term“responder device” may also refer to a responder STA.

Device D2 may request or initiate the ranging operation by transmittingan FTM request (FTM_REQ) frame to device D1. The FTM_REQ frame may alsoinclude a request for device D1 to capture timestamps (e.g., TOAinformation) of frames received by device D1 and to capture timestamps(e.g., TOD information) of frames transmitted from device D1. Device D1receives the FTM_REQ frame, and may acknowledge the requested rangingoperation by transmitting an acknowledgement (ACK) frame to device D2.The ACK frame may indicate whether device D1 is capable of capturing therequested timestamps. It is noted that the exchange of the FTM_REQ frameand the ACK frame is a handshake process that not only signals an intentto perform a ranging operation but also allows devices D1 and D2 todetermine whether each other supports capturing timestamps.

At time t_(a1), device D1 transmits a first FTM (FTM_1) frame to deviceD2, and may capture the TOD of the FTM_1 frame as time t_(a1). Device D2receives the FTM_1 frame at time t_(a2), and may capture the TOA of theFTM_1 frame as time t_(a2). Device D2 responds by transmitting an ACKframe to device D1 at time t_(a3), and may capture the TOD of the ACKframe as time t_(a3). Device D1 receives the ACK frame at time t_(a4),and may capture the TOA of the ACK frame at time t_(a4). At time t_(b1),device D1 transmits to device D2 a second FTM (FTM_2) frame thatincludes the timestamps captured at times t_(a1) and t_(a4) (e.g., theTOD of the FTM_1 frame and the TOA of the ACK frame). Device D2 receivesthe FTM_2 frame at time t_(b2), and may capture its timestamp as timet_(b2). Device D2 transmits an ACK frame to device D1 at time t_(b3).Device D1 receives the ACK frame at time t_(b4). This process maycontinue for any number of subsequent FTM and ACK frame exchangesbetween devices D1 and D2, for example, where device D1 embeds thetimestamps of a given FTM and ACK frame exchange into a subsequent FTMframe transmitted to device D2.

Upon receiving the FTM_2 frame at time t_(b2), device D2 has timestampvalues for times t_(a1), t_(a2), t_(a3), and t_(a4) that correspond tothe TOD of the FTM_1 frame transmitted from device D1, the TOA of theFTM_1 frame at device D2, the TOD of the ACK frame transmitted fromdevice D2, and the TOA of the ACK frame at device D1, respectively.Thereafter, device D2 may determine RTT as(t_(a4)−t_(a3))+(t_(a2)−t_(a1)). Because the RTT estimate does notinvolve estimating SIFS for either device D1 or device D2, the RTTestimate does not involve errors resulting from uncertainties of SIFSdurations. Consequently, the accuracy of the resulting estimate of thedistance between devices D1 and D2 is improved (e.g., as compared to theranging operation 300 of FIG. 3). A device may perform this rangingoperation with at least three other devices having known locations, anduse known trilateration techniques to estimate its location.

The accuracy of the RTT estimate between device D1 and device D2 may beproportional to the frequency bandwidth (e.g., the channel width) usedfor transmitting the FTM and ACK frames. As a result, ranging operationsfor which the FTM and ACK frames are transmitted using a relativelylarge frequency bandwidth may be more accurate than ranging operationsfor which the FTM and ACK frames are transmitted using a relativelysmall frequency bandwidth. For example, ranging operations performedusing FTM frame exchanges on an 80 MHz-wide channel are more accuratethan ranging operations performed using FTM frame exchanges on a 40MHz-wide channel, which in turn are more accurate than rangingoperations performed using FTM frame exchanges on a 20 MHz-wide channel.

In addition, because Wi-Fi ranging operations are typically performedusing frames transmitted as orthogonal frequency-division multiplexing(OFDM) symbols, the accuracy of RTT estimates may be proportional to thenumber of tones (e.g., the number of OFDM sub-carriers) used to transmitthe FTM and ACK frames between ranging devices. For example, while alegacy (e.g., non-HT) frame may be transmitted on a 20 MHz-wide channelusing 52 tones, an HT frame or VHT frame may be transmitted on a 20MHz-wide channel using 56 tones, and an HE frame may be transmitted on a20 MHz-wide channel using 242 tones. Thus, for a given frequencybandwidth or channel width, HT/VHT/HE frames use more tones than non-HTframes, and may therefore provide more accurate channel estimates andRTT estimates than non-HT frames. Accordingly, ranging operationsperformed with HT/VHT/HE frames may be more accurate than rangingoperations performed with non-HT frames.

The IEEE 802.11 REVmc standards allow FTM frames (e.g., the FTM_1 frame,the FTM_2 frame, and the FTM_3 frame of the example ranging operation400 of FIG. 4) to be transmitted using an HT format, a VHT format, an HEformat, and/or a legacy (e.g., non-HT) format. However, the IEEE802.11REVmc standards do not specify a particular format or protocol forACK frames transmitted during ranging operations. Typically, legacy ornon-HT ACK frames are (by default) transmitted by the initiator deviceduring FTM ranging operations (e.g., such as the example rangingoperation 400 of FIG. 4). Because non-HT ACK frames are transmittedusing fewer tones than ACK frames transmitted using HT, VHT, and HEformats, performing ranging operations using non-HT ACK frames mayundesirably limit the accuracy of such ranging operations. In addition,the IEEE 802.11ax standards target long delay spread channels foroutdoor wireless transmissions, and increase both the guard interval andthe OFDM symbol length (e.g., as compared with earlier protocols definedin the IEEE 802.11a/g/n/ac standards). The longer guard intervalsassociated with the IEEE 802.11ax standards may further increase theaccuracy of ranging operations performed using HE frame exchanges inlong delay spread channels.

Thus, it would be desirable to perform ranging operations using not onlyFTM frames transmitted using HT/VHT/HE formats but also using ACK framestransmitted using HT/VHT/HE formats, for example, to increase theaccuracy of ranging operations (e.g., as compared with the exampleranging operation 400 of FIG. 4). These are at least some of thetechnical problems to be solved by the example embodiments.

In accordance with the example embodiments, methods and apparatuses aredisclosed that may allow wireless devices to perform ranging operationsusing FTM and ACK frames transmitted in an HT, VHT, and/or HE format(e.g., rather than using, by default, non-HT ACK frames for rangingoperations). Because ACK frames in HT, VHT, and HE formats aretransmitted using more tones than non-HT ACK frames, ranging operationsin accordance with the example embodiments may achieve more accuratechannel estimates and/or more accurate RTT estimates than conventionalranging operations. Additional increases in ranging accuracy may beachieved by using HE ACK frames, which as mentioned above have longerguard intervals than other ACK frame formats. These and other details ofthe example embodiments, which provide one or more technical solutionsto the aforementioned technical problems, are described in more detailbelow.

FIG. 5A shows a signal diagram of a ranging operation 500 between afirst device D1 and a second device D2 in accordance with exampleembodiments, and FIG. 5B shows a sequence diagram 510 depicting theexample ranging operation 500 of FIG. 5A. Device D1 and device D2 mayeach be, for example, an access point (e.g., AP 110 of FIG. 1), astation (e.g., one of stations STA1-STA4 of FIG. 1), or another suitablewireless device (e.g., wireless device 200 of FIG. 2).

As the initiator device, device D2 may transmit an FTM_REQ frame todevice D1, the FTM_REQ frame requesting device D1 to perform a rangingoperation and indicating a number of types of non-legacy ACK frameformats supported by device D2 (512). More specifically, in someaspects, the FTM_REQ frame may include an ACK capabilities field thatindicates whether device D2 supports transmitting ACK frames in the HEformat, the VHT format, and/or the HT format (or any other suitablenon-legacy format). The ACK capabilities field, which may be includedwithin or appended to the FTM_REQ frame in any suitable manner, isdescribed in more detail below with respect to FIGS. 6-7. In otheraspects, the non-legacy ACK frame formats supported by device D2 may beindicated using a number of reserved bits of the FTM_REQ frame.

For at least one implementation in which device D2 is an access point,device D2 may indicate its non-legacy ACK frame format capabilities inbeacon frames. For example, beacon frames transmitted (e.g.,broadcasted) by device D2 may include an information element (IE) or avendor-specific information element (VSIE) that contains the non-legacyACK frame format capabilities of device D2. The IE or VSIE may beembedded within or appended to the beacon frame in any suitable manner.In other aspects, the non-legacy ACK frame formats supported by deviceD2 may be indicated using a number of reserved bits of the beacon frame.

For other embodiments, the FTM_REQ frame may indicate a preferred ordesired non-legacy ACK frame format (e.g., according to HE, VHT, or HTprotocols) and/or may request device D1 to transmit subsequent FTMframes using a selected non-legacy frame format (e.g., according to HE,VHT, or HT protocols). For these other embodiments, an indication of apreferred ACK frame format and/or an indication of a selected frameformat may be included within one or more capability fields includedwithin (or appended to) the FTM_REQ frame (or within a number ofreserved bits of the FTM_REQ frame).

Device D1 may receive the request to perform the ranging operation andthe non-legacy ACK frame formats supported by device D2 (513). Forexample, device D1 may receive the FTM_REQ frame, and decode informationcontained in the ACK capabilities field to determine whether device D2supports transmitting ACK frames in the HE format, the VHT format,and/or the HT format. Device D1 may respond to the request bytransmitting a response to device D2 (514). For some implementations,the response may be an ACK frame, as depicted in FIG. 5A. The ACK framemay acknowledge the requested ranging operation, may indicate whetherdevice D1 is capable of capturing timestamps, and/or may indicate anumber of ranging capabilities of device D1 (e.g., the ability toestimate angle of arrival information and/or angle of departureinformation). Device D2 may receive the response from device D1, anddecode the capabilities (if any) provided by device D1 (515).

Device D1 may determine whether it is capable of receiving thenon-legacy ACK frame formats supported by device D2, may transmit anFTM_1 frame indicating its capabilities to receive each of thenon-legacy ACK frame formats supported by device D2, and may record theTOD of the FTM_1 frame as time t_(a1) (516). More specifically, in someaspects, the FTM_1 frame may include an ACK capabilities field thatindicates whether device D1 supports receiving ACK frames in the HEformat, the VHT format, and/or the HT format (or any other suitablenon-legacy format). The ACK capabilities field, which may be includedwithin or appended to the FTM_1 frame in any suitable manner, isdescribed in more detail below with respect to FIGS. 7-8. In otheraspects, the non-legacy ACK frame formats supported by device D1 may beindicated using a number of reserved bits of the FTM_1 frame.

For at least one implementation in which device D1 is an access point,device D1 may indicate its non-legacy ACK frame format capabilities inbeacon frames. For example, beacon frames transmitted (e.g.,broadcasted) by device D1 may include an IE or VSIE that contains thenon-legacy ACK frame format capabilities of device D1. The IE or VSIEmay be embedded within or appended to the beacon frame in any suitablemanner. In other aspects, the non-legacy ACK frame formats supported bydevice D1 may be indicated using a number of reserved bits of the beaconframe.

Device D2 receives the FTM_1 frame from device D1 at time t_(a2),determines the non-legacy ACK frame format capabilities of device D1,and records the TOA of the FTM_1 frame as time t_(a2) (517).

Then, device D2 may select one of the non-legacy ACK frame formats or alegacy ACK frame format based, at least in part, on the indicatedcapabilities of device D1 (518). For example, if device D1 indicatesthat it is not capable of receiving any of the non-legacy ACK frameformats supported by device D2, then device D2 may select the legacy ACKframe format.

Conversely, if device D1 indicates that it is capable of receiving oneor more of the non-legacy ACK frame formats supported by device D2, thendevice D2 may select the non-legacy ACK frame format that achieves themost accurate channel estimates and/or the most accurate rangingaccuracy. For one example, if both device D1 and device D2 support theHE protocol, then device D2 may select the HE frame format fortransmitting ACK frames during the ranging operation. For anotherexample, if both device D1 and device D2 support the VHT protocol butnot the HE protocol, then device D2 may select the VHT frame format fortransmitting ACK frames during the ranging operation. For yet anotherexample, if both device D1 and device D2 support the HT protocol but notthe VHT or HE protocols, then device D2 may select the HT frame formatfor transmitting ACK frames during the ranging operation. Otherwise, ifdevice D1 does not support receiving ACK frames in any of the non-legacyACK frame formats, then device D2 may select the legacy (e.g., non-HT)frame format for transmitting ACK frames during the ranging operation.

In some aspects, device D2 may compare bits in the ACK capabilitiesfield of the received FTM_1 frame with corresponding bits in the ACKcapabilities field that was embedded within the FTM_REQ frame todetermine which of the non-legacy ACK frame formats are supported byboth device D1 and device D2, and then select the non-legacy ACK frameformat that results in the most accurate channel estimates and/or themost accurate ranging accuracy.

Device D2 then transmits an ACK frame in the selected frame format todevice D1 at time t_(a3), and records the TOD of the ACK frame as timet_(a3) (519). Device D1 receives the ACK frame from device D2 at timet_(a4), and records the TOA of the ACK frame as time t_(a4) (520).

Then, device D1 may embed a time value in an FTM_2 frame, and transmitthe FTM_2 frame to device D2 at time t_(b1) (521). For the example ofFIG. 5A, the time value is depicted as including the TOD of the FTM_1frame transmitted from device D1 (e.g., time t_(a1)) and the TOA of theACK frame received at device D1 (e.g., time t_(a4)). In other words,device D1 embeds the time stamps t_(a1) and t_(a4) into the FTM_2 frame.For other implementations, the time value may indicate a difference intime between the TOA of the ACK frame received at device D1 and the TODof the FTM_1 frame transmitted from device D1 (e.g.,t_(value)=t_(a4)−t_(a1)). In some aspects, device D1 may record the TODof the FTM_2 frame as time t_(b1).

Device D2 receives the FTM_2 frame at time t_(b2), and decodes theembedded time value (522). At this point, device D2 may determine thedistance between device D1 and device D2 (523). More specifically,device D2 may determine that it is a distance d=c*RTT/2 from device D1,where RTT=(t_(a4)−t_(a3))+(t_(a2)−t_(a1)).

Referring again to FIG. 5A, device D2 may transmit an ACK frame in theselected frame format to device D1 at time t_(b3) (e.g., to acknowledgereception of the FTM_2 frame). Device D1 receives the ACK frame at timet_(b4), and may record the TOA of the ACK frame as time t_(b4). DeviceD1 may embed another time value in an FTM_3 frame, and then transmit theFTM_3 frame to device D2 at time t_(b1). The time value embedded in theFTM_3 frame may indicate a difference time value equal to t_(b4)−t_(b1).This process may continue for any number of subsequent FTM and ACK frameexchanges between devices D1 and D2, for example, where device D1 embedsthe timestamps of a given FTM and ACK frame exchange into a subsequentFTM frame transmitted to device D2. In some aspects, ranging accuracymay improve as the number of FTM and ACK frame exchanges increases.

As described above, the example embodiments may allow an initiatordevice (e.g., device D2) to not only request a ranging operation with aresponder device (e.g., device D1) but also indicate a number of typesof non-legacy ACK frame formats supported by device D1. Becausenon-legacy ACK frames may be transmitted using more OFDM tones thanlegacy ACK frames, the example ranging operation 500 disclosed hereinmay achieve more accurate channel estimates and more accurate RTT valuesthan the example ranging operation 400 of FIG. 4. In addition, if bothdevice D1 and device D2 support HE ACK frames, then the example rangingoperation 500 may achieve even greater accuracy in long delay spreadchannels resulting from the longer guard intervals utilized by HE frametransmissions.

For other embodiments, the initiator device may not indicate its ACKframe format or protocol capabilities, but instead transmit ACK framesusing the same frame format used by the responder device to transmit thefirst FTM frame. For example, FIG. 5C shows a signal diagram of anotherranging operation 530 between device D1 and device D2 in accordance withexample embodiments, and FIG. 5D shows a sequence diagram 540 depictingthe example ranging operation 530 of FIG. 5C. Device D1 and device D2may each be, for example, an access point (e.g., AP 110 of FIG. 1), astation (e.g., one of stations STA1-STA4 of FIG. 1), or another suitablewireless device (e.g., wireless device 200 of FIG. 2).

As the initiator device, device D2 may transmit a request to perform aranging operation to device D1 (542). For some implementations, therequest may be an FTM_REQ frame, as depicted in FIG. 5C. Device D1 mayreceive the request to perform the ranging operation (543). As theresponder device, device D1 may respond to the request by transmitting aresponse to device D2 (544). For some implementations, the response maybe an ACK frame, as depicted in FIG. 5C. The ACK frame may acknowledgethe requested ranging operation, and may indicate a number of rangingcapabilities of device D1. Device D2 may receive the response fromdevice D1, and decode the capabilities (if any) provided by device D1(545).

After the above handshake process, devices D1 and D2 may exchange FTMand ACK frames to perform the ranging operation 530. Device D1 mayselect a frame format for subsequent FTM frames (546). For example,device D1 may select an HE frame format, a VHT frame format, or HT frameformat (or any other suitable non-legacy frame format). In some aspects,device D1 may embed an indication of the selected frame format into acapabilities field included within or appended to the FTM_1 frame.

Then, at time t_(a1), device D1 may transmit the FTM_1 frame in theselected frame format to device D2, and record the TOD of the FTM_1frame as time t_(a1) (547). Device D2 receives the FTM_1 frame fromdevice D1 at time t_(a2), determines the selected frame format of thereceived FTM_1 frame, and records the TOA of the FTM_1 frame as timet_(a2) (548). In some aspects, device D2 may determine the selectedframe format by decoding the preamble of the FTM_1 frame. In otheraspects, the selected frame format may be indicated in the FTM_1 frame(e.g., in a capabilities field included within or appended to the FTM_1frame). For still other aspects, device D1 may indicate the frame formatto be used during the ranging operation in one or more transmitted(e.g., broadcasted) beacon frames.

Device D2 then transmits an ACK frame in the selected frame format todevice D1 at time t_(a3), and records the TOD of the ACK frame as timet_(a3) (549). Thus, in accordance with some embodiments, device D2 mayautomatically transmit the ACK frame using the same frame format orprotocol used by device D1 to transmit the FTM_1 frame. For example, ifdevice D1 transmits the FTM_1 frame according to the HE protocol, thendevice D2 responds with HE ACK frames; if device D1 transmits the FTM_1frame according to the VHT protocol, then device D2 responds with VHTACK frames; if device D1 transmits the FTM_1 frame according to the HTprotocol, then device D2 responds with HT ACK frames. If device D2 doesnot support transmitting ACK frames in at least one of the non-legacyACK frame formats, then device D2 may transmit legacy ACK frames todevice D1 during the ranging operation.

Device D1 receives the ACK frame from device D2 at time t_(a4), andrecords the TOA of the ACK frame as time t_(a4) (550). Then, device D1may embed a time value in an FTM_2 frame, and transmit the FTM_2 frameto device D2 at time t_(b1) (551). As depicted in FIG. 5C, device D1 mayembed the timestamps t_(a1) and t_(a4) in the FTM_2 frame. For otherimplementations, the time value embedded in the FTM_2 frame may indicatea difference in time between the TOA of the ACK frame received at deviceD1 and the TOD of the FTM_1 frame transmitted from device D1 (e.g.,t_(value)=t_(a4)−t_(a1)). In some aspects, device D1 may record the TODof the FTM_2 frame as time t_(b1).

Device D2 receives the FTM_2 frame at time t_(b2), and decodes theembedded time value (552). At this point, device D2 may determine thedistance between device D1 and device D2 (553). The distance may bedetermined as d=c*RTT/2, where RTT=(t_(a4)−t_(a1))+(t_(a2)−t_(a1)).

FIG. 6 shows an example FTM_REQ frame 600 in accordance with exampleembodiments. The FTM_REQ frame 600 may be used in the example rangingoperation 500 of FIG. 5A and/or in the example ranging operation 530 ofFIG. 5C. The FTM_REQ frame 600 may include a category field 601, apublic action field 602, a trigger field 603, an optional location civicinformation (LCI) measurement request field 604, an optional locationcivic measurement request field 605, an optional FTM parameters field606, and an optional ACK capabilities field 607. The fields 601-606 ofthe FTM_REQ frame 600 are well-known, and therefore are not discussed indetail herein. In some aspects, the ACK capabilities field 607 may storeinformation indicating whether an initiator device (e.g., device D2 ofFIG. 5A) supports transmitting ACK frames in the HE format, the VHTformat, and/or the HT format (or any other suitable non-legacy format).In other aspects, information stored in the ACK capabilities field 607may indicate a specific ACK frame format preferred or selected by theinitiator device.

FIG. 7 depicts an example field 700 that may be one embodiment of theACK capabilities field 607 of the FTM_REQ frame 600 of FIG. 6. The field700 may include an Element ID field 701, a Length field 702, and an ACKcapabilities field 703. For at least one embodiment, the Element IDfield 701 may include one byte, the Length field 702 may include onebyte, and the ACK capabilities field 703 may include one byte (althoughfor other embodiments, other field lengths may be used). The Element IDfield 701 may store an element ID value indicating that field 700contains ACK capabilities for an associated device (e.g., for theinitiator device D2 of FIG. 5A). The Length field 702 may store a valueindicating a length (in bytes) of field 700. The ACK capabilities field703 may store information indicating whether the associated devicesupports the transmission of ACK frames in the HE format, the VHTformat, and/or the HT format. In some aspects, the ACK capabilitiesfield 703 may store a bitmap, for example, as depicted below in Table 1.

TABLE 1 Bit Value Indication 0 1 Supports ACK in HE format 0 Does notsupport ACK in HE format 1 1 Supports ACK in VHT format 0 Does notsupport ACK in VHT format 2 1 Supports ACK in HT format 0 Does notsupport ACK in HT format 3-7 0 reserved

As indicated above in Table 1, the value of bit 0 (b₀) may indicatewhether the associated device is capable of transmitting ACK frames inthe HE format, where b₀=1 indicates that the associated device supportsHE ACK frames, and b₀=0 indicates that the associated device does notsupport HE ACK frames. The value of bit 1 (b₁) may indicate whether theassociated device is capable of transmitting ACK frames in the VHTformat, where b₁=1 indicates that the associated device supports VHT ACKframes, and b₁=0 indicates that the associated device does not supportVHT ACK frames. The value of bit 2 (b₂) may indicate whether theassociated device is capable of transmitting ACK frames in the HTformat, where b₂=1 indicates that the associated device supports HT ACKframes, and b₂=0 indicates that the associated device does not supportHT ACK frames. The remaining bits, b₃-b₇, may be reserved. For otherimplementations, the relationship between bit positions in the examplebitmap of Table 1 and ACK frame formats or protocols may be differentthan depicted in the example of Table 1.

When a responder device (e.g., device D1 of FIG. 5A) receives an FTM_REQframe containing field 700, the responder device may decode the bitmapcontained in the ACK capabilities field 703 to determine which ACK frameformats are supported by the initiator device. As mentioned above, insome aspects, the ACK capabilities field 703 may indicate all of thenon-legacy ACK frame formats supported by the initiator device (e.g.,more than one of bits b₀-b₂ may be asserted to a logic high or “1”state). In response thereto, the responder device may indicate, to theinitiator device, its capabilities of receiving ACK frames transmittedin one or more of the non-legacy ACK frame formats supported by theinitiator device.

In other aspects, the ACK capabilities field 703 may indicate a desiredor preferred non-legacy ACK frame format that is supported by theinitiator device (e.g., only one of bits b₀-b₂ may be asserted to alogic high or “1” state). In response thereto, the responder device mayeither accept or reject the desired or preferred non-legacy ACK frameformat specified by the initiator device.

FIG. 8 depicts an example FTM frame 800, in accordance with exampleembodiments. The FTM frame 800 may be used in the example rangingoperation 500 of FIG. 5A and/or in the example ranging operation 530 ofFIG. 5C. The FTM frame 800 may include a category field 801, a publicaction field 802, a dialog token field 803, a follow up dialog tokenfield 804, a TOD field 805, a TOA field 806, a TOD error field 807, aTOA error field 808, an optional LCI report field 809, an optionallocation civic report field 810, an optional FTM parameters field 811,and an optional ACK capabilities field 812. The fields 801-811 of theFTM frame 800 are well-known, and therefore are not discussed in detailherein. The ACK capabilities field 812 may store information indicatingwhether a responder device (e.g., device D1 of FIG. 5A) is capable ofreceiving ACK frames transmitted in one or more non-legacy ACK frameformats.

The ACK capabilities field 812 of the FTM frame 800 may be the examplefield 700 depicted in FIG. 7. Thus, for at least some embodiments, theACK capabilities field 703 of field 700, when embedded within FTM frame800, may indicate the capabilities of the responder device to receiveACK frames transmitted using one or more of the non-legacy ACK frameformats supported by the initiator device. In some aspects, the FTMframe 800 (e.g., when used as the FTM_1 frame) may include an ACKcapabilities field 703 containing a bitmap depicted below in Table 2.

TABLE 2 Bit Value Indication 0 1 Supports ACK in HE format 0 Does notsupport ACK in HE format 1 1 Supports ACK in VHT format 0 Does notsupport ACK in VHT format 2 1 Supports ACK in HT format 0 Does notsupport ACK in HT format 3-7 0 reserved

As indicated above in Table 2, the value of bit 0 (b₀) may indicatewhether the responder device is capable of receiving ACK frames in theHE format, where b₀=1 indicates that the responder device is able toreceive HE ACK frames, and b₀=0 indicates that the responder device isnot able to receive HE ACK frames. The value of bit 1 (b₁) may indicatewhether the responder device is capable of receiving ACK frames in theVHT format, where b₁=1 indicates that the responder device is able toreceive VHT ACK frames, and b₁=0 indicates that the responder device isnot able to receive VHT ACK frames. The value of bit 2 (b₂) may indicatewhether the responder device is capable of receiving ACK frames in theHT format, where b₂=1 indicates that the responder device is able toreceive HT ACK frames, and b₂=0 indicates that the responder device isnot able to receive HT ACK frames. The remaining bits, b₃-b₇, may bereserved. For other implementations, the relationship between bitpositions in the bitmap and ACK frame formats or protocols may bedifferent than depicted in the example of Table 2.

FIG. 9 shows an example ACK frame 900 that may be used in accordancewith the example embodiments. In some aspects, the ACK frame 900 may beused as the ACK frames depicted in the example ranging operation 500 ofFIG. 5A and/or the example ranging operation 530 of FIG. 5C. The exampleACK frame 900 may include a 2-byte frame control field 901, a 2-byteduration field 902, a 6-byte receiver address (RA) field 903, and a4-byte frame control sequence (FCS) field 904. Although not shown inFIG. 9 for simplicity, the frame control field 901 may include a 2-bitframe Type field and a 4-bit Sub type field that together may storeinformation indicating that the example frame 900 of FIG. 9 is an ACKframe. For other embodiments, the field lengths of the example ACK frame900 may be of other suitable values. The duration field 902 stores avalue indicating a length of the ACK frame 900, the RA field 903 storesan address identifying the recipient of the ACK frame, and the FCS field904 stores a frame control sequence.

FIG. 10A shows an example preamble 1000A of a non-HT (e.g., legacy)frame within which the ACK frame 900 of FIG. 9 may be encapsulated, forexample, to transmit a non-HT ACK frame to a responder device duringranging operations disclosed herein (for simplicity, the frame body isnot shown in FIG. 10A). The preamble 1000A, which may be compliant withthe IEEE 802.11a/g standards, is shown to include a Legacy ShortTraining Field (L-STF) 1001, a Legacy Long Training Field (L-LTF) field1002, and a Legacy Signal (L-SIG) field 1003. A receiving device may useinformation contained in the L-STF 1001 for coarse frequency estimation,automatic gain control, and timing recovery, and may use informationcontained in the L-LTF 1002 for fine frequency estimation as well aschannel estimation and fine timing recovery. Information contained inthe L-SIG field 1003 may be used to convey modulation and codinginformation.

FIG. 10B shows an example preamble 1000B of an HT frame within which theACK frame 900 of FIG. 9 may be encapsulated, for example, to transmit anHT ACK frame to a responder device during ranging operations disclosedherein (for simplicity, the frame body is not shown in FIG. 10B). Thepreamble 1000B, which may be compliant with the IEEE 802.11n standards,is shown to include the L-STF 1001, L-LTF 1002, and L-SIG field 1003 ofFIG. 10A, as well as a first HT Signal (HT-SIG-1) field 1004, a secondHT Signal (HT-SIG-2) field 1005, an HT Short Training Field (HT-STF)1006, and an HT Long Training Field (HT-LTF) 1007. The HT-SIG fields1004-1005 may be used to convey modulation and coding information, aswell as the channel bandwidths, for HT transmissions. Informationcontained in the HT-STF 1006 may be used to improve automatic gaincontrol estimates for MIMO communications, and information contained inthe HT-LTF 1007 may be used to estimate MIMO channel conditions.

FIG. 100 shows an example preamble 1000C of a VHT frame within which theACK frame 900 of FIG. 9 may be encapsulated, for example, to transmit aVHT ACK frame to a responder device during ranging operations disclosedherein (for simplicity, the frame body is not shown in FIG. 100). Thepreamble 1000C, which may be compliant with the IEEE 802.11ac standards,is shown to include the L-STF 1001, L-LTF 1002, and L-SIG field 1003 ofFIG. 10A, as well as a set of VHT Signal-A (VHT-SIG-A) fields 1014 and1015, a VHT Short Training Field (VHT-STF) 1016, a VHT Long TrainingField (VHT-LTF) 1017, and a VHT Signal B (VHT-SIG-B) field 1018. TheVHT-SIG-A fields 1014-1015 may be used to convey modulation and codinginformation, channel bandwidths, SU-MIMO information, MU-MIMOinformation, beamforming information, and other suitable information forVHT transmissions. Information contained in the VHT-STF 1016 may be usedto improve automatic gain control estimates for SU-MIMO and MU_MIMOcommunications, and information contained in the VHT-LTF 1017 may beused to estimate various MIMO channel conditions. The VHT-SIG-B field1018 may include additional SU-MIMO and MU-MIMO information including,for example, user-specific information and the number of spatial streamsassociated with a given frame transmission.

FIG. 10D shows an example preamble 1000D of an HE frame within which theACK frame 900 of FIG. 9 may be encapsulated, for example, to transmit anHE ACK frame to a responder device during ranging operations disclosedherein (for simplicity, the frame body is not shown in FIG. 10D). Thepreamble 1000D, which may be compliant with the IEEE 802.11ax standards,is shown to include the L-STF 1001, L-LTF 1002, and L-SIG field 1003 ofFIG. 10A, as well as a Repeated Legacy Signal (RL-SIG) field 1024, a setof HE Signal-A (HE-SIG-A1/HE-SIG-A2) fields 1025, an HE Signal B(HE-SIG-B) field 1026, an HE Short Training Field (HE-STF) 1027, and anHE Long Training Field (HE-LTF) 1028. The HE-SIG-A1 and HE-SIG-A2 fields1025 may include parameters such as an indicated bandwidth, a payloadguard interval (GI), a coding type, a number of spatial streams (Nsts),a space-time block coding (STBC), beamforming information, and so on.Information contained in the HE-STF 1027 may be used to improveautomatic gain control estimates for SU-MIMO and MU_MIMO communications,and information contained in the HE-LTF 1028 may be used to estimatevarious MIMO channel conditions.

FIG. 11 is an illustrative flow chart 1100 depicting a second device D2requesting or initiating a ranging operation with a first device D1 inaccordance with example embodiments. Device D1 and device D2 may eachbe, for example, an access point (e.g., AP 110 of FIG. 1), a station(e.g., one of stations STA1-STA4 of FIG. 1), or other suitable wirelessdevice (e.g., wireless device 200 of FIG. 2). For the example operationof FIG. 11, device D2 is the initiator device, and device D1 is theresponder device.

First, device D2 may transmit, to device D1, an FTM_REQ frame indicatinga number of types of non-legacy ACK frame formats supported by device D2(1102). As discussed above, the non-legacy ACK frame formats may includeor otherwise be associated with a high efficiency (HE) protocol, a veryhigh throughput (VHT) protocol, and a high throughput (HT) protocol (orany other suitable non-legacy protocol). For some implementations, theFTM_REQ frame may be the FTM_REQ frame 600 of FIG. 6, and the indicationof the non-legacy ACK frame formats supported by device D2 may beembedded within the ACK capabilities field 607 of FTM_REQ frame 600. TheFTM_REQ frame may also include a request to initiate the rangingoperation (e.g., the ranging operation 500 of FIG. 5A). Device D2 mayreceive, from device D1, an ACK frame acknowledging receipt of theFTM_REQ frame (1104).

Next, device D2 may receive, from device D1, a first FTM frameindicating capabilities of device D1 to receive each of the number oftypes of non-legacy ACK frame formats supported by device D2 (1106). Forsome implementations, the first FTM frame may be the FTM frame 800 ofFIG. 8, and the indicated capabilities of device D1 may be embeddedwithin the ACK capabilities field 812 of FTM frame 800.

Device D2 may select one of the number of types of non-legacy ACK frameformats or a legacy ACK frame format based, at least in part, on theindicated capabilities of device D1 (1108). For example, if device D1indicates that it is not capable of receiving any of the non-legacy ACKframe formats supported by device D2, then device D2 may select thelegacy ACK frame format. Conversely, if device D1 indicates that it iscapable of receiving one or more of the non-legacy ACK frame formatssupported by device D2, then device D2 may select the non-legacy ACKframe format that is associated with the highest number of OFDM tonesand that is supported by device D1. In some aspects, device D2 maycompare bits in the ACK capabilities field of the received FTM framewith corresponding bits in the ACK capabilities field of the FTM_REQframe to determine which of the non-legacy ACK frame formats aresupported by both device D1 and device D2, and then select thenon-legacy ACK frame format that results in the most accurate channelestimates and/or the most accurate ranging accuracy.

Next, device D2 may transmit an ACK frame to device D1 in response toreception of the first FTM frame, the ACK frame transmitted using theselected ACK frame format (1110). In this manner, if the selected ACKframe format is an HE, VHT, or HT format, then the ranging operationbetween device D1 and device D2 may provide more accurate RTT estimatesthan conventional ranging operations that use legacy ACK frame formats(e.g., the example ranging operation 400 of FIG. 4).

Thereafter, device D2 may receive, from device D1, a second FTM frameincluding a time value indicative of a difference in time between thetime of arrival (TOA) of the ACK frame and the time of departure (TOD)of the first FTM frame (1112). Device D2 may then determine a distancebetween device D1 and device D2 based, at least in part, on the timevalue (1114).

Those of skill in the art will appreciate that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Further, those of skill in the art will appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the aspects disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the disclosure.

The methods, sequences or algorithms described in connection with theaspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

Accordingly, one aspect of the disclosure can include a non-transitorycomputer readable media embodying a method for time and frequencysynchronization in non-geosynchronous satellite communication systems.The term “non-transitory” does not exclude any physical storage mediumor memory and particularly does not exclude dynamic memory (e.g.,conventional random access memory (RAM)) but rather excludes only theinterpretation that the medium can be construed as a transitorypropagating signal.

While the foregoing disclosure shows illustrative aspects, it should benoted that various changes and modifications could be made hereinwithout departing from the scope of the appended claims. The functions,steps or actions of the method claims in accordance with aspectsdescribed herein need not be performed in any particular order unlessexpressly stated otherwise. Furthermore, although elements may bedescribed or claimed in the singular, the plural is contemplated unlesslimitation to the singular is explicitly stated. Accordingly, thedisclosure is not limited to the illustrated examples and any means forperforming the functionality described herein are included in aspects ofthe disclosure.

What is claimed is:
 1. A method of initiating a ranging operationbetween a first device and a second device, the method performed by thesecond device and comprising: transmitting, to the first device, a finetiming measurement (FTM) request frame indicating a number of types ofnon-legacy acknowledgement (ACK) frame formats supported by the seconddevice; receiving, from the first device, a first FTM frame indicatingcapabilities of the first device to receive each of the number of typesof non-legacy ACK frame formats supported by the second device;selecting one of the number of types of non-legacy ACK frame formats ora legacy ACK frame format based, at least in part, on the indicatedcapabilities of the first device; and transmitting an ACK frame to thefirst device in response to reception of the first FTM frame, the ACKframe transmitted using the selected ACK frame format.
 2. The method ofclaim 1, wherein the number of types of non-legacy ACK frame formatscomprises one or more members of the group consisting of a highefficiency (HE) protocol, a very high throughput (VHT) protocol, and ahigh throughput (HT) protocol, and the legacy ACK frame format comprisesa non-HT protocol.
 3. The method of claim 2, wherein the HE protocol iscompliant with an IEEE 802.11ax standard, the VHT protocol is compliantwith an IEEE 802.11ac standard, the HT protocol is compliant with anIEEE 802.11n standard, and the non-HT protocol is compliant with an IEEE802.11a/g standard.
 4. The method of claim 1, wherein the second deviceselects the legacy ACK frame format based on the first device indicatingan inability to receive any of the non-legacy ACK frame formatssupported by the second device.
 5. The method of claim 1, wherein thesecond device selects the non-legacy ACK frame format that is associatedwith the highest number of orthogonal frequency division multiplexing(OFDM) tones and that is supported by the first device.
 6. The method ofclaim 1, wherein the FTM request frame includes a capabilities fieldindicating the number of types of non-legacy ACK frame formats supportedby the second device.
 7. The method of claim 1, wherein the first FTMframe includes a capabilities field indicating which of the number oftypes of non-legacy ACK frame formats the first device is capable ofreceiving.
 8. The method of claim 1, further comprising: including, in abeacon frame, capability information indicating the number of types ofnon-legacy ACK frame formats supported by the second device; andtransmitting the beacon frame.
 9. The method of claim 8, wherein thecapability information is included within an information element (IE) ofthe beacon frame.
 10. The method of claim 1, further comprising:receiving, from the first device, a beacon frame indicating capabilitiesof the first device to receive one or more types of non-legacy ACK frameformats.
 11. The method of claim 1, further comprising: receiving, fromthe first device, a second FTM frame including a time value indicativeof a difference in time between a time of arrival (TOA) of the ACK frameand a time of departure (TOD) of the first FTM frame; and determining adistance between the first and second devices based, at least in part,on the time value.
 12. A second device to initiate a ranging operationwith a first device, the second device comprising: one or moreprocessors; and a memory configured to store instructions that, whenexecuted by the one or more processors, causes the second device to:transmit, to the first device, a fine timing measurement (FTM) requestframe indicating a number of types of non-legacy acknowledgement (ACK)frame formats supported by the second device; receive, from the firstdevice, a first FTM frame indicating capabilities of the first device toreceive each of the number of types of non-legacy ACK frame formatssupported by the second device; select one of the number of types ofnon-legacy ACK frame formats or a legacy ACK frame format based, atleast in part, on the indicated capabilities of the first device; andtransmit an ACK frame to the first device in response to reception ofthe first FTM frame, the ACK frame transmitted using the selected ACKframe format.
 13. The second device of claim 12, wherein execution ofthe instructions causes the second device to select the legacy ACK frameformat based on the first device indicating an inability to receive anyof the non-legacy ACK frame formats supported by the second device. 14.The second device of claim 12, wherein execution of the instructionscauses the second device to select the non-legacy ACK frame format thatis associated with the highest number of orthogonal frequency divisionmultiplexing (OFDM) tones and that is supported by the first device. 15.The second device of claim 12, wherein the FTM request frame includes acapabilities field indicating the number of types of non-legacy ACKframe formats supported by the second device.
 16. The second device ofclaim 12, wherein the first FTM frame includes a capabilities fieldindicating which of the number of types of non-legacy ACK frame formatsthe first device is capable of receiving.
 17. The second device of claim12, wherein execution of the instructions further causes the seconddevice to: include, in a beacon frame, capability information indicatingthe number of types of non-legacy ACK frame formats supported by thesecond device; and transmit the beacon frame.
 18. The second device ofclaim 17, wherein the capability information is included within aninformation element (IE) of the beacon frame.
 19. The second device ofclaim 12, wherein execution of the instructions further causes thesecond device to: receive, from the first device, a second FTM frameincluding a time value indicative of a difference in time between a timeof arrival (TOA) of the ACK frame and a time of departure (TOD) of thefirst FTM frame; and determine a distance between the first and seconddevices based, at least in part, on the time value.
 20. A non-transitorycomputer-readable storage medium storing one or more programs containinginstructions that, when executed by one or more processors of a seconddevice, cause the second device to initiate a ranging operation with afirst device by performing operations comprising: transmitting, to thefirst device, a fine timing measurement (FTM) request frame indicating anumber of types of non-legacy acknowledgement (ACK) frame formatssupported by the second device; receiving, from the first device, afirst FTM frame indicating capabilities of the first device to receiveeach of the number of types of non-legacy ACK frame formats supported bythe second device; selecting one of the number of types of non-legacyACK frame formats or a legacy ACK frame format based, at least in part,on the indicated capabilities of the first device; and transmitting anACK frame to the first device in response to reception of the first FTMframe, the ACK frame transmitted using the selected ACK frame format.21. The non-transitory computer-readable storage medium of claim 20,wherein execution of the instructions causes the second device to selectthe legacy ACK frame format based on the first device indicating aninability to receive any of the non-legacy ACK frame formats supportedby the second device.
 22. The non-transitory computer-readable storagemedium of claim 20, wherein execution of the instructions causes thesecond device to select the non-legacy ACK frame format that isassociated with the highest number of orthogonal frequency divisionmultiplexing (OFDM) tones and that is supported by the first device. 23.The non-transitory computer-readable storage medium of claim 20, whereinthe FTM request frame includes a capabilities field indicating thenumber of types of non-legacy ACK frame formats supported by the seconddevice.
 24. The non-transitory computer-readable storage medium of claim20, wherein the first FTM frame includes a capabilities field indicatingwhich of the number of types of non-legacy ACK frame formats the firstdevice is capable of receiving.
 25. The non-transitory computer-readablestorage medium of claim 20, wherein execution of the instructions causesthe second device to perform operations further comprising: including,in a beacon frame, capability information indicating the number of typesof non-legacy ACK frame formats supported by the second device; andtransmitting the beacon frame.
 26. A second device to initiate a rangingoperation with a first device, the second device comprising: means fortransmitting, to the first device, a fine timing measurement (FTM)request frame indicating a number of types of non-legacy acknowledgement(ACK) frame formats supported by the second device; means for receiving,from the first device, a first FTM frame indicating capabilities of thefirst device to receive each of the number of types of non-legacy ACKframe formats supported by the second device; means for selecting one ofthe number of types of non-legacy ACK frame formats or a legacy ACKframe format based, at least in part, on the indicated capabilities ofthe first device; and means for transmitting an ACK frame to the firstdevice in response to reception of the first FTM frame, the ACK frametransmitted using the selected ACK frame format.
 27. The second deviceof claim 26, wherein the second device is to select the legacy ACK frameformat based on the first device indicating an inability to receive anyof the non-legacy ACK frame formats supported by the second device. 28.The second device of claim 26, wherein the second device is to selectthe non-legacy ACK frame format that is associated with the highestnumber of orthogonal frequency division multiplexing (OFDM) tones andthat is supported by the first device.
 29. The second device of claim26, wherein the FTM request frame includes a capabilities fieldindicating the number of types of non-legacy ACK frame formats supportedby the second device.
 30. The second device of claim 26, furthercomprising: means for including, into a beacon frame, capabilityinformation indicating the number of types of non-legacy ACK frameformats supported by the second device; and means for transmitting thebeacon frame.